1. Field of the Invention
The present invention relates to an exposure method, an exposure apparatus and making method of the apparatus, and device and manufacturing method of the device. More particularly, the present invention relates to an exposure apparatus used in a photolithographic process in manufacturing a semiconductor device, liquid crystal display device, or the like and its making method, an exposure method using the exposure apparatus, a device manufacturing method using the exposure method and a device manufactured by the exposure apparatus.
2. Description of the Related Art
In a photolithographic process to manufacture a semiconductor device, liquid crystal display device, or the like, conventionally, a projection exposure apparatus such as a reduction projection exposure apparatus based on a step-and-repeat method (so-called stepper) or a scanning exposure apparatus based on a step-and-scan method (so-called scanning stepper) which is an improvement of the stepper is used.
The resolution of a projection optical system of a projection exposure apparatus of this type is expressed by the frequently cited Rayleigh criterion, R=kxc3x97xcex/N.A. In this case, R is the resolution of the projection optical system, xcexis the wavelength of exposure light, N.A. is the numerical aperture of the projection optical system, and k is the constant determined by the process as well as the resolution of the resist.
As the integration degree of semiconductor devices increases, a higher resolution is required for the projection optical system. In order to satisfy this demand, as is obvious from the equation above, efforts have been made to decrease the wavelength of exposure light or increase the numerical aperture of the projection optical system, i.e., to increase the N.A. In recent years, an exposure apparatus having a projection optical system with a numeral aperture of 0.6 or more and using krypton fluoride excimer laser (KrF excimer laser) with an output wavelength of 248 nm as an exposure light source has been put into practice, thus achieving exposure with a device rule (practical minimum line width) of 0.25 xcexcm.
In the conventional projection exposure apparatus described above, exposure amount control has been performed on the premise that the transmittance of the optical system does not change upon irradiation of exposure light. That is, the amount of exposure light irradiated on a reticle is measured by a light amount monitor (called an integrator sensor) arranged in the illumination optical system before the exposure light passes through the optical system. The amount of exposure light is also measured after the exposure light passes through the reticle and projection optical system by a light amount monitor, e.g., an illuminometer arranged on the wafer stage. The ratio between the output of the integrator sensor and the illuminometer is then calculated prior to exposure. And on exposure, by using the calculated ratio, the illuminance on the wafer surface (image plane) is estimated from the output value of the integrator sensor, and the exposure amount is feedback-controlled so that the illuminance on the image plane is determined at a desired
As a light source succeeding the krypton fluoride excimer laser, an argon fluoride excimer laser (ArF excimer laser) having an output wavelength of 193 nm is beginning to receive attention. If an exposure apparatus using this argon fluoride excimer laser as an exposure light source is put into practice, microdevices having fine patterns with a device rule of 0.18 xcexcm to 0.13 xcexcm can be expected to be mass-produced. Therefore, research and development on this technique have been vigorously conducted.
However, with exposure apparatus using an ArF excimer laser as an exposure light source, it was discovered that the transmittance of optical systems (illumination optical system and projection optical system) did change upon irradiation of exposure light at a level in which such changes cannot be neglected. According to recent researches, characteristics have been confirmed that the transmittance of an optical system gradually increases after starting irradiation of exposure light, and saturates when it comes to a certain level.
It is assumed that such changes occur due to a cleaning effect, i.e., removal of moisture and organic material from the surface of optical elements such as lenses and reflecting mirrors upon irradiation of ArF excimer laser light. Such a cleaning effect is also assumed to have occurred in the case of a KrF excimer laser light. With the case of an ArF excimer laser light, however, since the transmittance to substances such as water is low, the transmittance differs greatly when there are drops of water compared with the case when there are no drops of water. In the case of KrF excimer laser light, the difference is not very large, thus does not pose any serious problems.
Accordingly, the conventional exposure amount control method, based on the assumption that the transmittance of optical systems does not change upon irradiation of exposure light, now requires some kind of a modification.
The present invention has been made in consideration of this situation, and has as its first object to provide an exposure method, which can implement high-precision exposure without being influenced by variations in the transmittance of an optical system.
It is the second object of the present invention to provide an exposure apparatus, which can perform a highly precise exposure without being influenced by the variation in the transmittance of an optical system.
According to the first aspect of the present invention, there is provided a first exposure method performed by an exposure apparatus which has an optical system to transfer a pattern illuminated with exposure light from a light source onto a substrate, the method comprising: setting an exposure amount control target value in accordance with a transmittance of the optical system; and transferring the pattern onto the substrate through the optical system while an exposure amount is controlled based on the set exposure amount control target value.
In this case, an exposure amount control target value is xe2x80x9cnot a target exposure amount to be provided to an image plane (substrate surface) which is determined in accordance with the sensitivity of a resist coated on a substrate, but is the target value of an exposure amount which is to be controlled in order to provide the target exposure amount to the image planexe2x80x9d. In this specification, the term xe2x80x9cexposure amount control target valuexe2x80x9d is used in this sense.
According to this method, an exposure amount control target value is set in accordance with the transmittance of the optical system, and a pattern is transferred onto the substrate through the optical system while the exposure amount is controlled based on the set exposure amount control target value. That is, the exposure energy tone supplied to the image plane by unit area per unit time changes in accordance with the transmittance of the optical system. Therefore, as in the present invention, if an exposure amount control target value is set in accordance with the transmittance of the optical system and exposure is performed with the set exposure amount; highly precise exposure which is free from the influence of transmittance variations can be performed.
As a countermeasure for transmittance variations, the changes in transmittance can be measured in advance under the same illumination conditions as that of actual exposure, to obtain a transmittance time-varying curve. And on exposure, an elapsed time from the starting of irradiation and the period of time when the apparatus was not operating are measured with a timer. Then by using the time data and the transmittance time-varying curve, the transmittance can be estimated by calculation. By the calculation and an output from the light amount monitor arranged in the illumination optical system, the illuminance on the image plane is estimated, and the exposure amount can be controlled so as to set the illuminance on the image plane at a desired value. This method, however, requires a complicated preliminary measurement to obtain the transmittance time-varying curve, and in addition, the value estimated by calculation does not always coincide with the actual transmittance.
In the first exposure method according to the present invention, when the exposure amount control target value is set the transmittance of the optical system is a base to set the exposure amount control target value, and the transmittance can be actually measured at a predetermined measurement interval. In such a case, transmittance measurement is performed at a predetermined measurement interval. And until the next transmittance measurement is performed, the exposure amount control target value is set in accordance with a previously measured transmittance and the exposure amount is controlled based on the target value. Thus, the pattern illuminated with exposure light from the light source is transferred onto the substrate through the optical system. Accordingly, the complicated preliminary measurement described above is not required. In addition, since the exposure amount control target value is set according to the transmittance actually measured, and the exposure amount is controlled based on the target value, exposure with high precision can be performed. And as a result, the illuminance of the substrate surface (image plane illuminance) is always set at a desired (appropriate) value.
The transmittance of the optical system varies in different ways depending on the exposure condition. In consideration of this, in the first exposure method according to the present invention, the measurement interval is preferably set in accordance with an exposure condition. In such a case, the measurement intervals of the transmittance of the optical system are set in accordance with the exposure condition, and transmittance measurement is performed at the set measurement interval. And until the next transmittance measurement is performed, the exposure amount control target value is set in accordance with a previously measured transmittance and the exposure amount is controlled based on the target value. Thus, the pattern illuminated with exposure light from the light source is transferred onto the substrate through the optical system. According to the present invention, therefore, regardless of the exposure condition, exposure with high precision can be performed while the illuminance of the substrate surface (image plane illuminance) is always set at a desired (appropriate) value. In this case as well, the complicated preliminary measurement all described above, is not required.
The exposure condition is a condition serving as a reference for setting measurement intervals of the transmittance of the optical system. This exposure condition includes all conditions that influence the transmittance of the optical system. For example, the exposure condition may include a transmittance of a mask. Alternatively, the exposure condition may include one of a minimum line width and a permissible exposure amount error.
In the first exposure method according to the present invention, when the transmittance of the optical system, which serves as a reference for setting an exposure amount control target value, is actually measured at predetermined measurement intervals, the measurement interval may be changed in accordance with a variation amount between a transmittance obtained by a most recent transmittance measurement and a transmittance obtained by a measurement performed before the most recent measurement. In such a case, in accordance with the variation amount between the transmittance obtained by the most recent transmittance measurement and the transmittance obtained by a measurement performed before the most recent measurement, the measurement intervals are changed for subsequent transmittance measurements. Accordingly, short transmittance measurement intervals are set when the rate of change in transmittance is large and the transmittance needs to be frequently measured, whereas long transmittance measurement intervals are set when the rate of change in transmittance is small. This allows highly precise exposure amount control, without unnecessarily decreasing the throughput.
The inventors of the present invention analyzed the transmittance varying curves obtained by various experiments and discovered a predetermined relationship. The relationship exists between the transmittance time-varying of the optical system on exposure performed by an exposure apparatus using ArF excimer laser light (or illumination light having a shorter wavelength) as a light source, and the irradiation history of exposure light since the time when the apparatus was not operating.
In the first exposure method according to the present invention, the setting the exposure amount control target value may include a prediction function determining to determine a transmittance time-varying prediction function for the optical system in accordance with an irradiation history of exposure light on the optical system, and setting the exposure amount control target value based on the determined transmittance time-varying prediction function.
According to this method, a transmittance time-varying prediction function of the optical system is determined in accordance with the irradiation history of exposure light on the optical system, and an exposure amount control target value is set based on the determined transmittance time-varying prediction function. When transferring a pattern, the exposure amount is controlled based on the exposure amount control target value. Therefore, accurate exposure amount control (predictive control) can be performed in accordance with the transmittance predicted based on the transmittance time-varying prediction function. As a consequence, the image plane illuminance (substrate surface illuminance) can always be set at an almost desired value without unnecessarily decreasing the throughput.
The irradiation history of exposure light on the optical system is considered in the prediction function determining, because, as described above, the inventors found out in research that the rate of change (variation rate) in the transmittance of the optical system is dependent on the irradiation history of exposure light on the optical system. Accordingly, the transmittance time-varying prediction function in the present invention indicates an algebraic expression including a parameter dependent on the irradiation history of exposure light on the optical system.
The time-varying function can use a function expressed by                     T        =                  a          ·                      exp            ⁡                          (                                                ∑                                      i                    =                    1                                    k                                ⁢                                  xe2x80x83                                ⁢                bit                            )                                                          (        1        )            
in which T is the transmittance of the optical system, a is a parameter representing a rate of change in the transmittance, and bi is a parameter dependent on each exposure condition including an illumination condition.
The first exposure method according to the present invention can further comprise prior to the prediction function determining: measuring a period of time in which the exposure apparatus most recently stops operation; measuring an irradiation time of exposure light on the optical system in a self-cleaning operation which is performed after the exposure apparatus most recently stops operation; measuring an exposure light intensity; and measuring an irradiation amount.
In this specification, xe2x80x9cself-cleaningxe2x80x9d means a break-in to be performed after the start of the operation of the apparatus. While the operation of the apparatus is stopped, the surfaces of lens elements (the surfaces of optical thin films) configuring the optical system are contaminated with contaminants (organic substances and moisture). When performing a break-in, however, the optical system is irradiated with exposure light to produce the effect of gradually remove the contaminants from the surface of the lens elements (cleaning effect). So, naturally, as to distinguish this operation from the cleaning effect also evident during exposure, the operation is not referred to simply as cleaning.
The irradiation history is determined in accordance with the above respective physical quantities during when the apparatus not operating, and when actual exposure on the substrate starts. Therefore, an accurate exposure amount prediction function can be determined by obtaining the irradiation history. And the irradiation history can be obtained by actually measuring a period of time in which the exposure apparatus most recently stops operation; measuring an irradiation time of exposure light on the optical system in a self-cleaning operation which is performed after the exposure apparatus most recently stops operation; measuring an exposure light intensity; and measuring an irradiation amount.
In the first exposure method according to the present e invention, it is more preferable that the environmental conditions for the optical system is measured at a cl, predetermined time interval, and the environmental conditions are considered when transmittance time-varying prediction function is determined. This is because by the research of the inventors of the present invention, it has been discovered that the environmental conditions such as the temperature and humidity in the chamber where the exposure apparatus body is housed, and the atmospheric pressure and CO2 concentration in the lens chamber in the optical system, e.g., a projection optical system, affect the rate of change of the transmittance of the optical system.
In the first exposure method according to the present invention, the method may further comprise: measuring a transmittance of the optical system at a predetermined interval, and can correct the transmittance time-varying prediction function each time a transmittance measurement is performed. This is because it is difficult to accurately and completely predict the transmittance time-varying of the optical system. Therefore, to allow a more accurate exposure amount control, the changes in transmittance are measured at a predetermined interval, and the errors in the predictive values of exposure amounts are also corrected in the predetermined interval.
In this case, it is preferable that the predetermined interval of the measuring the transmittance is determined in respect to a relationship with a required exposure precision. In such a case, when a required exposure precision is extremely high, the measurement intervals are shortened to correct a transmittance time-varying prediction function at shorter intervals, as a result, further reducing an error in the calculated predictive value of transmittance. In contrast to this, when a required exposure precision is low, to prevent an unnecessary decrease in throughput, the measurement interval is prolonged.
Also, since the transmittance varies in different manners (rate of change), the interval of the measuring the transmittance may be shortened when a rate of change in the transmittance of the optical system is large, and prolonged when the rate of change in the transmittance of the optical system is small. This makes it possible to prevent an unexpected decrease in throughput while maintaining a highly precise exposure amount control.
According to the second aspect of the present invention, there is provided a second exposure method to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the method comprising: setting measurement intervals in accordance with an exposure condition; and measuring a variation in the amount of the exposure light passing through the optical system in the set measurement intervals.
In this case, the exposure condition may include at least one of an illumination condition to illuminate a mask, a transmittance of the mask, a minimum line width, and a permissible exposure amount error.
According to the third aspect of the present invention, there is provided a third exposure method to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the method comprising: measuring a variation in the amount of the exposure light passing through the optical system in a predetermined measurement interval; and changing the predetermined measurement intervals upon the measuring, in accordance with a comparison result of a variation of a first measurement of the light amount and a variation of a second measurement of the light amount.
In this case, the first and second measurements may be performed prior to starting of exposure. Alternatively, the first and second measurements may be performed after starting of exposure.
According to the fourth aspect of the present invention, there is provided a fourth exposure method performed by an exposure apparatus to transfer a pattern illuminated from a light source with exposure light through an optical system onto a substrate, the method comprising: a self-cleaning to clean the optical system by irradiating the optical system with the exposure light on a predetermined condition prior to exposure; a prediction function determining to determine a transmittance time-varying prediction function of the optical system in consideration of the predetermined condition; and setting the exposure amount control target value based on the determined transmittance time-varying in prediction function.
In this case, the prediction function determining can take into consideration the period of time in which the operation of the apparatus is stopped. The predetermined condition may also include an irradiation time of the exposure light on the optical system, the exposure light intensity, and an irradiation amount.
According to the fifth aspect of the present invention, there is provided a fifth exposure method to transfer a pattern illuminated from a light source with exposure light through an optical system onto a substrate, the method comprising: setting a measurement interval in accordance with an exposure condition; and measuring an amount of the exposure light passing through the optical system in the measurement interval.
In this case, the method can further comprise: obtaining a transmittance of the optical system in accordance with an amount of the exposure light which is measured before passing through the optical system, and the measurement result of the exposure light passing through the optical system.
According to the sixth aspect of the present invention, there is provided a first exposure apparatus to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the exposure apparatus comprising: an exposure amount setting unit to set an exposure amount control target value in accordance with a transmittance of the optical system; and an exposure amount control system connected with the exposure amount setting unit to control an exposure amount based on the set exposure amount control target value.
According to this apparatus, the exposure amount setting unit sets an exposure amount control target value in accordance F with the transmittance of the optical system. The exposure amount control system controls the exposure amount based on the set exposure amount control target value during transfer of a pattern onto the substrate through the optical system (i.e., during exposure). As described above, exposure energy provided to a unit area per unit time in an image plane changes in accordance with the transmittance of the optical system. If, as in the present invention, the exposure amount control target value is set in accordance with the transmittance of the optical system, and the exposure amount is controlled based on the target value, the illuminance of a substrate surface (image plane illuminance) can always be set at a desired (appropriate) value. Thus, exposure with high precision can be achieved.
In the first exposure apparatus according to the present invention, when the apparatus further comprises; a transmittance measurement unit which measures a transmittance of the optical system, the exposure amount setting unit can set the exposure amount control target value in accordance with the transmittance measured by the transmittance measurement unit. In such a case, the transmittance measurement unit measures the transmittance of the optical system, and the exposure amount setting unit sets an exposure amount control target value in accordance with the measured transmittance. When transferring a pattern, the exposure amount control system controls the exposure amount based on the set exposure amount control target value. Accordingly, any complicated preliminary measurement, as when performed to obtain the transmittance time-varying curve is not required. In addition, since the exposure amount is controlled based on the exposure amount control target value set by the transmittance actually measured, exposure with high precision can be performed while the illuminance of a substrate surface (image plane illuminance) is always set at a desired (appropriate) value.
In this case, the transmittance measurement unit may perform the transmittance measurement at a predetermined measurement interval. In such a case, the transmittance measurement unit performs transmittance measurement at a predetermined measurement interval. Until the next transmittance measurement, the exposure amount control target value is set by the exposure amount setting unit in accordance with the transmittance most recently measured, and during exposure, the exposure amount control system controls the exposure amount based on the set exposure amount control target value. Accordingly, the complicated preliminary measurement is not required. In addition, the exposure amount control target value is set according to the transmittance actually measured, and the exposure amount is controlled based on the set exposure amount control target value. And, each time the transmittance is re-measured, the exposure amount target value is updated and set in accordance with the renewed transmittance, and the exposure amount is controlled based on the updated exposure amount control target value. Therefore, the illuminance of the substrate surface (image plane illuminance) can always be set at a desired (appropriate) value, while reducing the influence of transmittance variation, thereby making it possible to perform exposure with high precision.
The transmittance of the optical system varies in different manners depending on the exposure condition. In consideration of this, the first exposure apparatus according to the present invention preferably further comprises: a control unit to set the measurement interval of the transmittance measurement unit in accordance with an exposure condition. In such a case, the control unit sets the measurement interval of the transmittance of the optical system in accordance with the exposure conditions, and the transmittance measurement unit performs transmittance measurement at the set measurement interval. Until the next transmittance measurement, the exposure amount control target value is set by the exposure amount setting unit in accordance with the transmittance most recently measured. And when a pattern is transferred onto the substrate through the optical system, the exposure amount is controlled by the exposure amount control system based on the set exposure,amount control target value. If the exposure conditions are changed while exposure is performed, the control unit updates and sets the measurement interval of the transmittance measurement unit in accordance with the exposure conditions after the change. Subsequently, transmittance measurement is performed at the measurement intervals after the change. Accordingly, if the exposure conditions are likely to cause large transmittance variations, short transmittance measurement intervals can be set, and if exposure conditions are likely to cause moderate transmittance variations, long transmittance measurement intervals can be set. Therefore, exposure with high precision can be performed regardless of changes in exposure conditions, without being influenced by transmittance variations, and without unnecessarily decreasing the throughput. In this case as well, the complicated preliminary measurement is not required.
In the case the first exposure apparatus according to the present invention includes a control unit to set measurement intervals of the transmittance measurement unit in accordance with exposure conditions, when the apparatus further comprises: an information reading unit to read information of a mask on which the pattern is formed, the control unit may automatically determine measurement intervals for the transmittance measurement unit based on the information of the mask read by the information reading unit.
The first exposure apparatus according to the present invention may further comprise: a control unit connected with the transmittance measurement unit to set the transmittance measurement interval of the transmittance measurement unit in accordance with a variation amount between a transmittance obtained by a most recent transmittance measurement and a transmittance obtained by a measurement performed before the most recent measurement, the respective measurement performed by the transmittance measurement unit. In such a case, the control unit sets the transmittance measurement intervals of the transmittance measurement unit in accordance with the variation amount between a transmittance obtained by a most recent transmittance measurement and a transmittance obtained by a measurement performed before the most recent measurement. Therefore, in the case the rate of change in transmittance is high and transmittance measurement must be frequently performed, short transmittance measurement intervals are set. And, in then case the rate of change in transmittance is low, long transmittance measurement intervals are set, thus, allowing exposure with high precision without unnecessarily decreasing the throughput.
In this case, two sequential measurements of transmittance by the transmittance measurement unit can be performed prior to starting of exposure. Alternatively, two sequential measurements of transmittance by the transmittance measurement unit can be performed after starting of exposure. In the former case, the transmittance measurement interval can be automatically set in accordance with the transmittance of the optical system prior to exposure. In the latter case, as described above, the transmittance measurement interval can be automatically set so that the transmittance measurement interval is short when the rate of change in transmittance is high, and transmittance measurement interval is long when the rate of change in transmittance is low, after the exposure starts.
In the first exposure apparatus according to the present invention, the transmittance measurement unit may include, for example, a first optical sensor disposed in a light path of the exposure light to detect the amount of exposure light irradiated on the pattern, a second optical sensor arranged to be substantially flush with the substrate, and a control unit connected with the first optical sensor and the second optical sensor to detect the amount of exposure light passing through the optical system by using the second optical sensor at a timing which corresponds to an exposure condition, and to obtain a transmittance of the optical system based on the amount of exposure light and an output from the first optical sensor.
In such a case, when it becomes a predetermined timing corresponding to the exposure condition, the control unit detects the amount of light having passed through the optical system using the second optical sensor arranged to be almost flush with the substrate. It then obtains the transmittance of the optical system based on the light amount and the output from the first optical sensor. The exposure amount setting unit then sets (updates) the exposure amount control target value in accordance with the measured (obtained) transmittance. The exposure amount during the transfer of the pattern is controlled based on the updated exposure amount control target value by the exposure amount control system. This makes it possible to perform exposure with high precision without being influenced by the variation in the transmittance of the optical system.
In this case, as well, it is preferable that the exposure At amount control system controls the exposure amount based on the exposure amount control target value and the output from the first optical sensor when transferring the pattern onto the substrate.
In this case, the timing to detect the amount of exposure light having passed through the optical system to update the exposure amount control target value may be determined in accordance with the exposure condition which influence the transmittance of the optical system. For example, the control unit may detect the amount of exposure light having passed through the optical system at a timing which corresponds to a transmittance of the mask on which the pattern is formed. Alternatively, the control unit may detect the amount of exposure light having passed through the optical system at a timing set in consideration of one of a minimum line width and a permissible exposure amount error.
In the first exposure apparatus according to the present invention, when the apparatus further comprises: a first optical sensor disposed in the light path of the exposure light to detect the amount of exposure light illuminated on the pattern, it is preferable that the exposure amount control system controls the exposure amount based on the exposure amount control target value and an output from the first optical sensor when transferring the pattern onto the substrate. In such a case, by obtaining the actual exposure amount based on the light amount detected by the first optical sensor, and by feedback-control to reduce the difference (deviation) between the exposure amount and the exposure amount control target value to zero, exposure amount control with high accuracy can be performed.
In the first exposure apparatus according to the present invention, when the apparatus further comprises: a calculation unit to determine a transmittance time-varying prediction function of the optical system in accordance with an irradiation history of exposure light on the optical system, the exposure amount setting unit may set the exposure amount control target value based on the transmittance time-varying prediction function determined by the calculation unit.
According to this apparatus, the calculation unit determines a transmittance time-varying prediction function of the optical system in accordance with an irradiation history of exposure light on the optical system. And based on the determined transmittance time-varying prediction function, the exposure amount setting unit sets the exposure amount control target value. When the pattern is transferred, the exposure amount is controlled based on the set exposure amount control target value by the exposure amount control system. Therefore, accurate exposure amount control (predictive control) can be performed in accordance with the predicted transmittance based on the transmittance time-varying prediction function, without frequently performing transmittance measurement during exposure. Patterns can be transferred onto the substrate by using the optical system while the image plane illuminance (substrate surface illuminance) is always set at an almost desired value. Therefore, exposure with high precision can be performed, without being influenced by changes in the transmittance of the optical system.
In this case, the apparatus can further comprise: a transmittance measurement unit to measure the transmittance of the optical system at a predetermined interval; and a correction unit connected with the calculation unit to correct the transmittance time-varying prediction function each time the transmittance measurement is performed. In such a case, when the transmittance measurement unit measures the transmittance of the optical system, the correction unit can correct the transmittance time-varying prediction function each time such measurement is performed. As a consequence, errors in exposure amount predictive values are corrected at the predetermined interval, thus allowing a more accurate exposure amount control.
In this case, the apparatus can further comprise: a control unit connected with the transmittance measurement unit to set the transmittance measurement interval of the transmittance measurement unit in accordance with a variation amount between a transmittance obtained by a most recent transmittance measurement and a transmittance obtained by a measurement performed before the most recent measurement, the measurement performed by the transmittance measurement unit. In such a case, when the rate of change in transmittance is high and a transmittance needs to be frequently measured, short transmittance measurement intervals are set. And when the rate of change in transmittance is low, long transmittance measurement intervals are set. Thereby allowing exposure with high precision without decreasing unnecessarily the throughput.
In the first exposure apparatus according to the present invention, it can further comprise: a mask stage disposed between the illumination optical system and the projection optical system to hold the mask on which the pattern is formed; and a substrate stage disposed in an image plane side of the projection optical system to hold the substrate, wherein the optical system includes an illumination optical system disposed in an optical path of the exposure light to illuminate the mask on which the pattern is formed with the exposure light, and a projection optical system disposed in the optical path of the exposure light to project the exposure light which exits from the mask onto the substrate. With this apparatus, the mask held on the mask stage is illuminated with exposure light from the illumination optical system, and the pattern on the mask is transferred onto the substrate on the substrate stage through the projection optical system. In this case, as described above, the exposure amount control target value is set in accordance with the transmittance of the optical system, and when transferring the pattern, the exposure amount is controlled based on the set exposure amount control target value. This makes it possible to provide a static type exposure apparatus such as a stepper, which can perform exposure with high precision while always setting the illuminance of the substrate surface (image plane illuminance) at a desired (appropriate) value.
In this case, the apparatus can further comprise; a driving unit connected with the mask stage and the substrate to synchronously move the mask stage and the substrate stage in a linear direction perpendicular to an optical axis of the projection optical system. In such a case, a scanning projection exposure apparatus which can perform exposure with high precision while always setting the illuminance of the substrate surface (image plane illuminance) at a desired (appropriate) value without being influenced by transmittance variations can be provided.
According to the seventh aspect of the present invention, there is provided a second exposure apparatus to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the exposure apparatus comprising: a measurement unit to measure a variation in an amount of exposure light passing through the optical system; and a control unit connected with the measurement unit to change intervals of the measurement performed by the measurement unit in accordance with an exposure condition.
In this case, the structure of the measurement unit can include a first optical sensor disposed in an optical path of the exposure light to detect the amount of exposure light irradiated on the pattern, and a second optical sensor arranged to be substantially flush with the substrate.
According to the eighth aspect of the present invention, there is provided a third exposure apparatus to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the exposure apparatus comprising: a measurement unit to measure a variation in an amount of exposure light passing through the optical system; and a control unit connected with the measurement unit to change an interval of a measurement performed by the measurement unit, in accordance with a comparison result of a variation of a first measurement of the light amount and a variation of a second measurement of the light amount.
According to the ninth aspect of the present invention, there is provided a fourth exposure apparatus to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the exposure apparatus comprising: a unit which communicates with the optical system to self -clean the optical system by irradiating the optical system with the exposure light in a predetermined condition before starting of exposure; a calculation unit connected with the unit to determine a transmittance time-varying prediction function of the optical system in consideration of the predetermined condition; and an exposure amount setting unit connected with the calculation unit to set an exposure amount control target value based on the determined transmittance time-varying prediction function.
According to the tenth aspect of the present invention, there is provided a fifth exposure apparatus to transfer a pattern illuminated with exposure light from a light source onto a substrate through an optical system, the exposure apparatus comprising: a measurement unit to measure an amount of exposure light passing through the optical system at a predetermined interval; and a control unit connected with the measurement unit to set the interval of a measurement performed by the measurement unit in accordance with an exposure condition.
According to the eleventh aspect of the present invention, there is provided a method of making an exposure apparatus to transfer a pattern of a mask onto a substrate, the method comprising: providing an illumination optical system to irradiate the mask with exposure light; providing a projection optical system to project the exposure light emitted from the mask onto the substrate; providing a substrate stage to hold the substrate; providing an exposure amount setting unit to set an exposure amount control target value in accordance with a transmittance of the projection optical system; and providing an exposure amount control system to control an exposure amount based on the exposure amount control target value.
According to this method, the exposure apparatus of the present invention can be produced by mechanically, optically, and electrically combining and adjusting the illumination optical system, projection optical system, substrate stage, exposure amount setting unit, exposure amount control system, and various other components. In this case, a static type exposure apparatus based on the step-and-repeat method can be produced.
The method of producing an exposure apparatus according to the present invention can further comprise: providing a mask stage to hold the mask; and providing a driving unit to synchronously move the mask stage and the substrate stage on respective planes parallel to a linear direction perpendicular to an optical axis of the projection optical system. In this case, for example, a scanning exposure apparatus based on the step-and-scan method can be produced, which can control the exposure amount by changing and adjusting the relative scanning velocity of the mask stage and substrate stage.
In a lithographic process, when exposure is performed using the exposure method in the present invention, a plurality of layers of patterns can be formed on a substrate with high overlay accuracy. This makes it possible to manufacture micro devices with a higher integration degree and a high yield, thus improving the productivity. Likewise, by performing exposure using the exposure apparatus of the present invention in the lithographic process, the exposure amount control precision is improved, and hence the line width control precision is improved. Therefore, a plurality of layers of pattern can be formed on a substrate with high overlay accuracy. Consequently, this allows manufacturing of microdevices with a higher integration degree and a high yield, thus improving the productivity. Thus, according to another aspect, the present invention is a device manufacturing method using the exposure method of the present invention or the exposure apparatus of the present invention, and a device manufactured by the manufacturing method.